The duration of the study is 5 days, with 2 testing periods lasting 2 days each. During one of the periods, the study participants will breathe nitric oxide mixed with room air through a face mask during the tests. During the other period, the participants will breathe room air alone through a face mask during the tests. At least 1 day will separate the treatment periods. During each of the 2 treatment periods (nitric oxide and room air), participants will undergo 4 tests to determine whether the treatment improves the heart's response to stress with increased heart rate and contraction. Approximately one hour before each of the tests, participants will breathe either nitric oxide mixed with room air or room air alone through the face mask, and continue the inhalation treatment while each test is being performed. The face mask will be removed at the end of each test.